db7 1998 not ticking over

I assume it's the 6-cylinder model.. try cleaning the throttle body and idle control valve.

Remove from car and degrease, then give them a good soaking in carb cleaner.

Let it soak in and keep repeating until everything looks clean inside.

Also check air filter and fuel pump / rail pressure if possible.

have a look at the 2 3/8 outer dia black vacuum pipes that run from the inlet manifold to the sensor on the l/h wing,they have a nasty habit of perishing although usually on older 7s